Tree: How to keep opened states when tree updated

I need to keep tree nodes open/closed stated when i set new data to this.dataSource.data. New data is very same with old - it just have one or several lowest-level nodes added/removed.

My idea is to record node expansion to ReplaySubject and replay expansion queue. It should work but it's very ugly way.

I hope that here are have much more elegant way to solve my problem.

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